TRestEventSelectionProcess upgrade

[AlvaroEzq]

Adding new possibility of using the TRestEventSelectionProcess without an external fileWithIDs by evaluating the conditions on the TRestAnalysisTree of the processing file itself.

[DavidDiezIb]

I guess this was to include the selection process in the processing chain, right? Before it was only possible from existing files, not in the middle of the processing chain, am I correct?

[AlvaroEzq]

I guess this was to include the selection process in the processing chain, right? Before it was only possible from existing files, not in the middle of the processing chain, am I correct?

Yes!

[lobis]

@AlvaroEzq I approve the PR but made some minor changes which shouldn't modify the behaviour:

• std::string are already initialized as "", no need to explicitly do it.
• Don't use new / delete if it can be avoided, in this case you can just create a regular (stack allocated) TRestRun which will be deleted when existing the scope.
• Whenever you can try to use {} for all if statements and such, in my experience not using them for single-line expressions usually leads to mistakes down the road.